This invention is preferably a power supply from a System on Chip (SOC) to a secure digital (SD) memory card embodied in a standard UHS-1 card interface. These SD memory cards come in several standard voltage/frequency ratings. It is advantageous for the SOC to be able to operate with any connected SD memory card and be capable of changing the supplied power supply voltage based upon the memory card requirements.
The UHS-1 memory card interface permits these operating modes:
TABLE 1ModeNameVoltageSpeed (MHz)DSDefault Speed3.325HSHigh Speed3.350SDR12Single Data Rate1.825SDR25Single Data Rate1.850SDR50Single Data Rate1.8100SDR105Single Data Rate1.8208DDR50Dual Data Rate1.850
FIG. 1 illustrates a simplified view of the UHS-1 standard manner of the SOC selecting the voltage and data rate for the SD memory card. Program 100 begins with detection of SD memory card insertion in decision block 101. This detection generally triggers an interrupt to service the card interface. If a card insertion is not detected (No at decision block 101), then the system returns to decision block 101 and continues to wait for detection of SD memory card insertion. If card insertion is detected, (Yes at decision block 101), then the system supplies 3.3 volt power to the SD memory card at block 102.
The SOC and the SD memory card then communicate to set the voltage and speed of the interface (block 103). The result is determined by the SOC is a communications mode including supply voltage and frequency. This typically occurs by the SOC transmitting a series of commands to the SD memory card and making a communications mode decision bases upon the SD memory card responses. The interface frequency is not relevant to this invention and is not illustrated.
Relevant to this invention is the determined supply voltage for the SD memory card. Decision block 104 determines if the selected voltage for the SD memory card is 3.3 volts or 1.8 volts. If the determined power supply voltage is 3.3 volts, then program continues with other processing at continue block 105. If the determined power supply is 1.8 volts, then block 106 changes the electric power supplied to the SD memory card to 1.8 volts. Then program continues with other processing at continue block 105.
The prior art employed a separate power supply module between the SOC and the SD memory card. This separate power supply module required a separate power rail and an interface to the SOC to control the supplied voltage. This involves a separate control bus (typically an I2C bus) and programming in the SOC to control the power supply module via this separate bus. This introduces additional overhead in code and time delay in the power supply control operation. This also presents problems in the input/output (I/O) of the SOC to the SD memory card. If the SOC uses a low geometry process which does not support 3.3V transistors, this prior art requires an additional supply rail to create an intermediate bias of the SOC I/O circuits.